Various sign devices of the above type are known. Such signs are used both as permanent signs and as signs, where the user according to his wishes can replace the information-carrying part with another information-carrying part. These sign devices are generally used without any locking of the information-carrying part in relation to the mounting part, for which reason unauthorized persons can easily remove the information-carrying part. Different methods have consequently been used for locking the two parts together, but the previously known methods have not proved fully satisfactory, either because the information-carrying part has been disfigured by visible screws or because unauthorized persons have nevertheless been able to release the fastening mechanism concerned.